https://issues.dlang.org/show_bug.cgi?id=22988

Dennis <dkorpel@live.nl> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |dkorpel@live.nl
         Resolution|---                         |INVALID

--- Comment #1 from Dennis <dkorpel@live.nl> ---
Because AddExpression has precedence over ShiftExpression, it's parsed as:
```
enum b = a ? 1 << (a - 1) : 0;
```
Since a = 0, it results in a shift by -1, which gives an error. To fix, add
parentheses around the shift:
```
enum b = a ? (1 << a) - 1 : 0;
```

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https://issues.dlang.org/show_bug.cgi?id=22988

Max Samukha <maxsamukha@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |---

--- Comment #2 from Max Samukha <maxsamukha@gmail.com> ---
The precedence is intended to be (a ? (1 << (a - 1)) : 0).

Since 'a' is 0, the first branch of the conditional shouldn't be evaluated, and the expected result is 0.

Compare that to the runtime version, which behaves as expected:

void main()
{
    int a = 0;
    int b = a ? 1 << a - 1 : 0;
    assert(b == 0);
}

--

https://issues.dlang.org/show_bug.cgi?id=22988

--- Comment #3 from Max Samukha <maxsamukha@gmail.com> ---
Similar case:

enum l = 0;
enum int[l] a = [];
enum b = l ? a[l] : 0;

Error: array index 0 is out of bounds `a[0 .. 0]`


Or simply:

enum a = 0 ? 1 << -1 : 0;

enum int[0] a = [];
enum b = 0 ? a[0] : 0;

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https://issues.dlang.org/show_bug.cgi?id=22988

--- Comment #4 from Max Samukha <maxsamukha@gmail.com> ---
(In reply to Max Samukha from comment #3)

> enum b = l ? a[l] : 0;

Should be:
enum b = l ? a[l - 1] : 0;

--

https://issues.dlang.org/show_bug.cgi?id=22988

Dennis <dkorpel@live.nl> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Error: shift by -1 is       |no short-circuiting when
                   |outside the range `0..31`   |constant folding ternary
                   |                            |operator

--- Comment #5 from Dennis <dkorpel@live.nl> ---
Ah, thanks for clearing that up. I think this test illustrates the problem
best:
```
enum a = false && (1 << -1); // passes
enum b = false ? (1 << -1) : 0; // fails

```
I've updated the title

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https://issues.dlang.org/show_bug.cgi?id=22988

--- Comment #6 from Max Samukha <maxsamukha@gmail.com> ---
(In reply to Dennis from comment #5)

> ```
> I've updated the title

Great, thanks!

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https://issues.dlang.org/show_bug.cgi?id=22988

Dlang Bot <dlang-bot@dlang.rocks> changed:

           What    |Removed                     |Added
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           Keywords|                            |pull

--- Comment #7 from Dlang Bot <dlang-bot@dlang.rocks> ---
@BorisCarvajal created dlang/dmd pull request #13961 "Fix Issue 22988 - no short-circuiting when constant folding ternary operator" fixing this issue:

- Fix Issue 22988 - no short-circuiting when constant folding ternary operator

https://github.com/dlang/dmd/pull/13961

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https://issues.dlang.org/show_bug.cgi?id=22988

Dlang Bot <dlang-bot@dlang.rocks> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #8 from Dlang Bot <dlang-bot@dlang.rocks> ---
dlang/dmd pull request #13961 "Fix Issue 22988 - no short-circuiting when constant folding ternary operator" was merged into master:

- befbc46fd7309ffb6e640822fa74280a750cf65e by Boris Carvajal:
  Fix Issue 22988 - no short-circuiting when constant folding ternary operator

https://github.com/dlang/dmd/pull/13961

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